1. Field of the Invention
This invention relates to copper catalysts useful for the selective hydrogenation of the linolenate moiety of polyunsaturated vegetable oil.
2. Description of the Prior Art
It is frequently desirable to reduce the triunsaturated linolenic component of vegetable oils to a more saturated state. For example, soybean oil contains 6 to 9% of the linolenic moiety, which is suspected of causing flavor reversion. The stability of soybean oil as it relates to flavor could be vastly improved by eliminating the linolenate from the oil. This is preferably accomplished by hydrogenating it to the nutritionally desirable linoleic moiety.
Nickel catalysts currently used for the hydrogenation are highly active but also nonselective. That is, they simultaneously reduce both the linolenic and the linoleic components at a relative rate of about 2:1.
Commercially available copper-chromites are by far more selective than the nickel catalysts in that they reduce the linolenic moiety at 10-15 times the rate of linoleic reduction. However, commercial copper-chromites are not as active as the nickel catalysts, and are therefore uneconomical to use.
It is generally known in the prior art that the activity of catalysts can be increased by supporting them on high surface area supports, such as the silica gels taught in U.S. Pat. Nos. 3,515,678 and 3,749,681. These gels are generally manufactured by first acidifying sodium silicate to precipitate it. The precipitate is then aged under carefully controlled conditions to aggregate the molecules. These aggregates are subsequently washed, formed by specialized procedures into the desired shape, and dried. The gel properties are particularly influenced by the precipitation and aging conditions. Most procedures for manufacturing silica gel are proprietary and usually expensive. Therefore, despite the superior activity over the copper-chromites, the advantage of catalysts supported on such gels is negated by the prohibitive cost of the special supports.
An attempt to substitute sodium silicate for the costly silica gel support is taught by Koritala [JAOCS 45(3): 197-200 (1968)]. The sodium silicate was precipitated from aqueous solution with approximately an equal molar amount of copper nitrate. Neither the activity nor the selectivity was comparable to the supported catalysts, and it was generally unacceptable for commercial use.